1. Language of Motion

2. 8.1 Direction Makes a Difference
Two main types of quantities:
Scalars: Describe magnitude (size of a measurement) but not direction.
Example: Johnny skateboarded 7 meters, Johnny skateboarded for 5 seconds.
Distance - describes the length between 2 locations
Vectors: Describe magnitude and direction.
Example: Johnny skateboard 7 m East
Position - a specific point relative to a point of origin
Time interval (change in time)
The time interval to move from the fire hydrant to the sign is calculated by:
final minus the initial

3. Displacement describes how much an object’s position has changed.
A car leaves home and drives 10 km to the store then returns home, what is its distance and displacement?
The car has driven a total distance of 20 km but its final displacement is 0 km.
Displacement describes how much an object’s position has changed.
If the car leaves home and drives 10 km east to the store, what is its displacement?
= 10 km [E] - 0
= 10 km [E]
= + 10 km
When using vector quantities, opposite directions are given opposite signs.

4. What is the person’s displacement & distance travelled between 0s and 15s?
d = 15 m + 10 m + 20 m
= 45 m
= 10 m [W] – 5 m [E]
= m – (+5 m)
= m
= 15 m [W]

5. Think you got it? Try This…
What is her initial position?
What is the distance she travelled?
What is the time interval?
What is her displacement from hydrant?
d= 9 m [E]
d= + 9 m
d = 14 m
t = 10 sec
Δ d = 5 m [W]
Δ d = - 5 m

6. Can create a table as follows:
When a body covers equal distances in equal intervals of time then the body is said to have uniform motion.
Roll a ball across a floor…
1 s
2 s
3 s
4 s
5 s
0 m
20 cm
60 cm
100 cm
Can create a table as follows:
Uniform motion creates a straight line on a position-time graph
TIME (s)
POSITION (cm) 1 20 2 40 3 60 4 80 5
100
Objects in uniform motion do not speed up, slow down or change direction

7. Which direction is the object moving?
Forward
On a position-time graph, the slope is equal to the velocity:
A positive slope means moving away from origin at a uniform speed
Zero slope means the object’s average velocity is zero (i.e. the object isn’t moving!)
A negative slope means that the object’s average velocity is moving in the negative direction (i.e. the object is moving backwards at a uniform speed)
Which direction is the object moving?
Since right is given as a positive value, then a negative slope indicates the object is travelling to the left.

8. 8.2 Average Velocity
On a position-time graph the average velocity is the slope of the line
Average Velocity of ball????
the rise is the change in position ( ) divided by the run which is the change in time ( ).
vav = 80 cm - 40 cm
4 s - 2 s
= 40 cm
2 s
= 20 cm/s

9. Comparing Velocity Who is running faster and by how much?
va = 16 m - 12 m
4 s - 3 s
= 4 m 1s
= 4 m/s
vb = 10 m - 8 m
6 s - 4 s
= 2 m
2 s
= 1 m/s
va - vb = 4 m/s – 1 m/s
= 3 m/s

10. Calculating Velocity
Speed - is relationship between the distance of an object per unit of time (scalar quantity), e.g. 60 km/h
Velocity is a relationship between the displacement (speed and direction) of an object per unit of time (vector quantity), e.g. 60 km/h [N]
Displacement & relationship between velocity, and time is given by:
Time & relationship between displacement and velocity is given by:

11. Calculating Velocity
1) A boat is at rest and travels 280 m east in a time of 120 s. What is the boat’s average velocity?
Vav = ∆d/∆t = 280 m east / 120 s = 2.33 m/s east
2) A person, originally at the starting line, runs west at 6.5 m/s. What is the runner’s displacement after 12 s?
∆d = vav * ∆t = 6.5 m/s * 12 s = 78 m
3) A car is driving forward at 15 m/s. How long would it take this car to pass through an intersection that is 11 m long?
∆t = ∆d/vav = 11 m / 15 m/s = s
4) A car is travel at 30 m/s east and slows down to 20 m/s east in 5 s. What is the cars average velocity over those 5 s?
Average velocity = V V2 = 30 m/s + 20 m/s = 25 m/s 2
5) You drive 500 km east in 5 hours and 300 km east in 3 hours. What is the car’s average velocity?
(500 km Km ) / 8 hours = km/h